In a UMTS (Universal Mobile Telecommunications System) network, system features that are based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access) for the purposes of improving the spectral efficiency and improving the data rate. For this UMTS network, long-term evolution (LTE) has been under study for the purposes of further increasing high-speed data rates, providing low delay and so on.
In the third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. In a system of the LTE scheme, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. In the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems of LTE have been under study as well (for example, LTE-Advanced (LTE-A)). For example, in LTE-A, there is a plan to expand the maximum system band according to LTE specifications, which is 20 MHz, to approximately 100 MHz. In LTE-A, the maximum number of transmitting antennas according to LTE specifications is planned to be expanded from four antennas to eight antennas.
In a system of the LTE scheme, a MIMO (Multi Input Multi Output) system is proposed (see, for example, non-patent literature 1), as a radio communication technique to transmit and receive data by a plurality of antennas and improve the data rate (spectral efficiency). In the MIMO system, a plurality of transmitting/receiving antennas are provided in the transmitter/receiver, so that different transmission information sequences are transmitted from different transmitting antennas at the same time. On the receiver side, taking advantage of the fact that fading variation is produced differently between the transmitting/receiving antennas, it is possible to increase the data rate (spectral efficiency) by separating and detecting the information sequences that have been transmitted at the same time.
In a system of the LTE scheme, single-user MIMO (SU-MIMO) transmission, in which transmission information sequences that are transmitted from different transmitting antennas at the same time are all directed to the same user, and multiple-user MIMO (MU-MIMO) transmission, in which transmission information sequences that are transmitted from different transmitting antennas at the same time are directed to different users, are defined. In these SU-MIMO transmission and MU-MIMO transmission, on the receiver side, an optimal PMI is selected from a codebook, in which a plurality of amounts of phase/amplitude control (precoding matrix (precoding weights)) to be set in the antennas of the transmitter and PMIs (Precoding Matrix Indicators) that are associated with this precoding matrix, are defined, and this is fed back to the transmitter as channel information (CSI: Channel State Information). On the transmitter side, precoding for each transmitting antenna is performed based on the PMI fed back from the receiver, and transmission information sequences are transmitted.